The present invention relates to techniques for signal transmission between devices such as multiprocessors or memories (for example, digital circuits constructed of CMOS's or between their functional blocks) in an information processing apparatus and more particularly, to a technique of increasing the speed of bus transmission in which a plurality of devices are connected to the same transmission line and data transfer is carried out between the devices. Especially, the present invention is concerned with a bus for connecting a plurality of memory modules and a memory controller and a system using the bus.
As a bus system connected with many nodes to perform high-speed data transfer, a non-contact bus wiring line has been known as disclosed in U.S. Pat. No. 5,638,402 (JP-A-7-141079). A fundamental system of this type is shown in FIG. 2. In the system, data transfer between two nodes is effected using a crosstalk generation portion or directional coupler having a length of L. More particularly, in the known transfer technique, data transfer between a bus master 10-1 and slaves 10-2 to 10-3 is carried out using crosstalk between two lines, that is, between a terminated wiring line 1—1 and terminated wiring lines 1-2 and 1-3 each having a length of L. This is suited to one to multiple inter-transfer such as data transfer between the single bus master 10-1 and the plural slaves 10-2 and 10-3 and is suitably applied to data transfer between a memory controller and memories.
In the prior art disclosed in U.S. Pat. No. 5,638,402 (JP-A-7-141079) assigned to the present assignee, however, the line length L occupied by the directional coupler determines the pitch between the bus slaves 10-2 and 10-3. In FIG. 2, the wiring length occupied by the two bus slaves DRAM's 10-1 and 10-2 is 2L at the minimum and the pitch between the DRAM's amounts up to L.
A simple way to increase the density in the system, that is, to decrease the pitch between the DRAM's is to shorten the wiring length L of the directional coupler but this expedient leads to a decrease in transmission efficiency or coupling degree and therefore, the pitch cannot be reduced to below a predetermined value, for example, 30 mm.